Achieving crop fertilization by timing the release or application of fertilizer nutrients is known. Fertilization in the container-grown wholesale plant industry, for example, has been accomplished by methods including:                Multiple applications of granular fertilizer        Overhead liquid application of soluble fertilizers        Incorporating slow release fertilizers into potting soil        Polymer coated fertilizers.        
Each of these methods has associated drawbacks. In granular fertilizers, excessive moisture rapidly dissolves granular fertilizer, resulting in uncontrolled amounts of fertilizer being made available to the plant all at once. This forces growers to leach the soil to protect their plants from highly soluble salts, leaching fertilizer from the plant. The result is increased labor and fertilization costs, as well as an adverse impact on the environment.
Overhead liquid application of water-soluble fertilizers presents similar problems. The overhead application is inefficient since the liquid fertilizer falls between the plant containers. The result is multiple applications, waste, and harmful elevated nutrient runoff.
Slow release fertilizers delay the dissolution of the fertilizer substrate. Most slow release fertilizers, however, are not dependable in adverse environmental conditions such as high heat and moisture. Hot and wet conditions can cause slow release fertilizers to flash release, causing damage to both the plant material and the environment.
Prior art methods include encapsulating a fertilizer having a given chemical composition or compound such that the nutrients are released over a period of time. For example, coated urea has been used as a source of time released nitrogen, which is a nutrient that promotes plant height and leaf formation in a plant. U.S. Pat. Nos. 5,147,442, 5,560,768 and 6,500,223 each of which is incorporated in its entirety, illustrate such coated fertilizers and methods associated with them.
Encapsulated slow-release fertilizers may be classified into two major groups according to the fertilizer release mechanism:
(i) A first group in which the release is governed by the rate of water permeation through a polymeric or copolymeric membrane of the water-proofing material, and by the rate of fertilizer diffusion away from each coated particle into the surrounding soil. Typical examples of membrane material in slow-release fertilizers of this group are copolymers or glyceryl esters of unsaturated acids with dicyclopentadiene (U.S. Pat. No. 3,223,518), epoxy-polyester resins (U.S. Pat. No. 3,259,482), urethanes (U.S. Pat. No. 3,264,089) and polystyrenes (U.S. Pat. No. 3,158,462).
(ii) A second group with relatively thick encapsulating coats, in which release is governed mainly by rupture of the coat, a typical example being particulate fertilizers with sulfur based encapsulation. The rupture occurs upon the permeation of water into the coated particles as a result of the osmotic pressure that builds up within. The sulfur based coating in slow-release fertilizers of this second group are generally produced by spraying onto the particulate fertilizer a molten sulfur based material as disclosed, for example, in U.S. Pat. No. 4,857,098
Prior art methods of slowly releasing fertilizer nutrients fail to achieve efficient utilization by a crop or plant since differing stages of crop growth require different nutrients. For example, even though polymer coated fertilizers can be coated with a resin to slow fertilizer release, a drawback of these products is that they are typically a coated compound at set ratios which do not match the physiological needs of the plant and the timing of the crop. For example, prior art polymer coated fertilizers which are coated with a resin do not match all physiological needs of the plant and the timing of the crop, since the release of all nutrients is set to occur at the same time, as determined by the compound analysis of the fertilizer prill.
In another example, potassium enhances plant development at the bloom stage, and is best fed to the plant even after the release of nitrogen is substantially complete. Consequently early releasing potassium is redundant as the element is not PRIMARILY needed at the early stage. An early releasing coated nitrogen, or other early releasing coated nutrient or nutrient compound, directed at feeding root development has not simultaneously been an efficient source of potassium. Inefficient or multiple applications of potassium is required by prior art methods.
Further, extreme environmental conditions can cause both the polymer coated fertilizers described at (i) and (ii) above to release both too fast and too inconsistently, which results in damage to plant material as well as requiring multiple applications. Inefficient fertilization, missed applications, and additional labor costs from multiple applications increase costs and losses with respect to crops. What is needed is a method of delivering the proper single elements of nitrogen, phosphorous and potassium as nutrition to plants in the differing stages of plant growth without the need for multiple applications of fertilizer.